2. 2 But what makes the electrons flow? Any electrical circuit requires three things 1.A source 2.A load 3.A means of transmission A definition of a current a flow of electrons can be simplified to `a flow of electrons’

3. 3 The source provides an electromotive force or e.m.f. to the circuit The e.m.f. is the drive or push that is applied to the circuit to force the current around the circuit Symbol is E the unit is volt (V)

4. Here we have,  a source - the single cell  a load - the bit we want to use  wires linking the source to the load 4 volt droppotential difference. If we were to measure the voltage lost across the load we would call this the volt drop or potential difference.

5. 5. In the simple circuit the e.m.f is the same as the voltage that we would measure across the load. The e.m.f provides the force that drives the current around the circuit. The circuit may have several loads connected to it, then the e.m.f. would be the sum of all of the potential differences.

6. 6 The sum of the voltages dropped across each resistor should give the same value as the source e.m.f. Although e.m.f. and volt drop or potential difference are measured in volts the symbol is different. Volt-drop or potential difference; Symbol U, unit Volt (V) Generated e.m.f. or battery e.m.f.; Symbol E, unit Volt (V)

7. 7 Resistance is the opposition to the current flow This is one of the most important formula In 1827 George Simon Ohm discovered that if you have metal, maintained at a constant temperature for a constant length and area, and if you then increase the voltage the current increases in the same proportion. He discovered that resistance of the conductor linked the voltage to the current.

8. 8 This is the Ohm’s Law Triangle giving V = I X R, I = V/R, and R = V/I This is one of the most important formula